The present invention relates to a radiation image information read-out system, and more particularly to a radiation image erase unit for use with a stimulable phosphor sheet in such a radiation image information read-out system having a read-out unit, wherein the radiation image erase unit disposed near the read-out unit is a unitary structure, simple and small in overall construction, and arranged to prevent erasure light from leaking toward the read-out unit.
There has in recent years been proposed radiation image recording and reproducing system in which a radiation image of an object can be produced by using a stimulable phosphor. The stimulable phosphor, when exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, stores a part of the energy of the radiation. When the stimulable phosphor exposed to the radiation is exposed to stimulating rays such as visible light, the stimulable phosphor emits light in proportion to the stored energy of the radiation. The radiation image recording and reproducing system employs such a stimulable phosphor. More specifically, the radiation image of an object such as a human body is stored in a sheet having a stimulable phosphor (hereinafter referred to as a "stimulable phosphor sheet" or a "phosphor sheet"), and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is photoelectrically detected and converted to an electric image signal which is processed to reproduce a visible image on a recording medium such as a photographic light-sensitive material or on a display unit such as a cathode ray tube (CRT). The aforesaid radiation image information recording and reproducing system is disclosed in Japanese Laid-Open Patent Publication. No. 55-12429 or 56-11395, for example.
The irradiation image recording and reproducing system of the type described above is of greater practical advantage than conventional radiographic systems using a combination of an intensifying screen and an X-ray film in that images can be recorded in a wide range of radiation exposure. More specifically, it is known that the amount of light emitted from a stimulable phosphor upon stimulation thereof is proportional in a highly wide range to the amount of radiation to which the stimulable phosphor has been exposed. Therefore, even if the amount of radiation to which the stimulable phosphor is exposed varies widely under various conditions, radiation images free from such exposure variations can be obtained by selecting a suitable read-out gain in the photoelectric transducer for reading and converting the emitted light into an electric signal, and processing the electric signal into a visible image on a recording medium such as photographic light-sensitive material or on a display unit such as a CRT.
The radiation image recording and reproducing system is capable of processing a converted electric signal to produce a visible image on a recording medium or a display unit so that the radiation image can well be observed for diagnostic purpose. In this system, the stimulable phosphor sheet does not serve as a final image recording medium, but as a temporary image storage medium for eventually transferring images to the final recording medium or display unit. Therefore, the stimulable phosphor sheet can be used repeatedly, and is economical and convenient if in repetitive use.
To reuse the stimulable phosphor sheet, the residual radiation energy on the stimulable phosphor sheet after the radiation image has been read out by stimulating rays is discharged by exposure to light having a wavelength within the stimulating wavelength for the stimulable phosphor constituting the stimulable phosphor sheet, and the stimulable phosphor sheet is ready again for recording a radiation image thereon. The erasure of the radiation energy from the stimulable phosphor sheet is disclosed in U.S. Pat. No. 4,400,619, Japanese Laid-Open Patent Publication No. 56-11392 or 56-12599, for example.
A radiation image read-out system designed to meet the above requirement includes an image read-out unit for reading out an image which has been stored in a reusable stimulable phosphor sheet by exposing it to a radiation passing through an object, and an image erasure unit for discharging residual radiation energy from the stimulable phosphor sheet after the image has been read out so as to allow the stimulable phosphor sheet to be reused for recording a next radiation image. With the image read-out unit and the image erasure unit combined into one system, the system is compact in size and can be installed in a small space, and hence it is quite practical and convenient in use.
In such a radiation image read-out system, the image read-out unit and the image erasure unit should preferably be disposed as closely to each other as possible for making system compact. However, if the image read-out unit and the image erasure unit were positioned so closely to each other that there would be no space therebetween, then certain problems would arise. When the stored image is to be read out, the stimulable phosphor sheet is exposed to stimulating rays to cause it to emit light in the pattern of the stored image, and the interior of the image read-out unit should be kept as dark as possible. The image erasure unit houses therein a light source which is as intensive as possible for discharging all of the remaining radiation energy stored in the stimulable phosphor sheet. If any light from the image erasure unit leaked into the image read-out unit positioned closely to the image erasure unit, then the image could not be read out accurately by the image read-out unit, and no accurate radiation image could not be obtained.